Although there is considerable interest in immunity to schistosomes, few antigens have been well-characterized. Preparations of culture secretory antigens and surface membrane antigens have both been shown to be extremely heterogeneous mixtures. While both protein and carbohydrate fractions from adult worms have been partially characterized, much remains to be done since no single surface antigen has been isolated and characterized completely. We do not yet know whether any of the surface proteins found on adult worms are present on the infective stage of the parasite, and the possibility that antigens are shared by different schistosome species remains conjectural. Attempts to immunize animals with crude extracts of worm material have met with only limited success. In this regard, purified fractions of surface antigens might be more efficacious as a potential vaccine. In addition to their vaccine potential, purified fractions of surface antigens could be used to produce monospecific antisera which would be invaluable for future experimental work. In order to further characterize surface antigens on S. mansoni: I. Surface proteins from several stages of schistosomula will be radio-iodinated, and the results will be compared to those previously obtained for adult worms. II. Surface glycoproteins from adults and schistosomula will be characterized using carbohydrate radiolabeling methods. III. Tegumental proteins extracted from adult S. mansoni will be isolated and fractionated using preparative electrophoresis and isoelectric focusing techniques.